Over the recent years various demands regulating the behaviour of for example wind turbine facilities during grid faults have been suggested. Recent grid demands require that wind turbine facilities remain connected to the grid during over voltage grid events and at the same time support the grid during such events.
EP 2 704 309 A2 discloses a method for controlling a dual-fed induction generator (DFIG) in response to an over voltage grid event. The method involves that an output of a closed-loop portion of a rotor current regulator is set to a fixed value such that a predictive feed-forward path sets an internal voltage for the DFIG. Moreover, the method involves that a condition of a high DC voltage on a DC link or a condition predictive of high DC voltage on the DC link is detected, and in response a rotor related current command is reduced to approximately zero. Thus, the method suggested in EP 2 704 309 A2 aims at protecting the DFIG during the over voltage grid event by setting the rotor related current command to approximately zero. It is a disadvantage of this approach that even though the DFIG is protected during the over voltage grid event the grid itself is not supported appropriately during the event.
It may be seen as an object of embodiments of the present invention to provide a method for supporting the grid during an OVRT event.
It may be seen as a further object of embodiments of the present invention to provide a method for maintaining a grid-side inverter fully operable during an OVRT event.
It may be seen as an even further object of embodiments of the present invention to provide a method for ensuring that a grid-side inverter is capable of injecting both active and reactive power into an associated grid during an OVRT event.